1. Field of the Invention
The present invention relates to a stereoscopic electronic circuit device in which circuit boards mounted with electronic components are connected stereoscopically with each other by using a relay board or the like, and also relates to a shield structure thereof.
2. Background Art
In recent years, as electronic devices have been reduced in size and weight, there has been a strong demand for improving mounting density in electronic circuit devices having resistors, capacitors, semiconductor elements and the like mounted on an insulating circuit board. In addition, as electronic devices have been operated at higher speed and frequency, there have been rigorous demands for satisfying the criteria of EMC (Electromagnetic Compatibility) which indicates the ability to avoid malfunction due to external electromagnetic waves or not to interfere with the operation of other electronic devices.
Conventionally, in electronic circuit devices of this kind, high-density component mounting has been achieved by reducing the interconnection pitch to a micro level or stacking a plurality of electronic circuit boards.
FIG. 30 shows an electronic circuit device, which is disclosed in Japanese Patent Laid-Open Application No. 2001-177235 (hereinafter referred to as patent document 1).
In this device, spacer 1360, which is temporarily fixed with solder balls 1380 and 1390 conducting between the top and bottom surfaces of spacer 1360 through via holes 1320, is temporarily fixed between base printed board 1310 and module circuit board 1350. Then, batch reflow soldering is performed to stack module circuit board 1350 mounted with surface mounting component 1330, semiconductor bare chip 1340 and other components onto base printed board 1310 with spacer 1360 disposed therebetween.
FIG. 31 shows another electronic circuit device, which is disclosed in Japanese Patent Laid-Open Application No. 2001-267715 (hereinafter referred to as patent document 2). In this device, heat-resistant elastic member 1400 whose outer surface is coated with conductive material is soldered to connecting land 1420 of one electronic circuit board 1410 and is bonded with pressure to connecting land 1440 of the other electronic circuit board 1430 by clips, bolts or the like. Thus, electronic circuit boards 1410 and 1430 each mounted with surface mounting component 1450, semiconductor bare chip 1460 and the like are vertically stacked.
FIG. 32 shows further another electronic circuit device, which is disclosed in Japanese Patent Laid-Open Application No. H06-260736 (hereinafter referred to as patent document 3). In this device, an IC module, which is composed of module circuit board 1500 mounted with IC package 1510 and passive components 1520 and 1530, is connected mechanically and electrically to mother board 1540 with connecting chip 1550 disposed therebetween.
In addition to the aforementioned structures, board bonding can also be achieved by using connectors which are general connecting components.
However, while electronic devices are becoming higher performing and miniaturized, there is a limit to improving mounting density in two-dimensional electronic circuit devices only by reducing the interconnection pitch to a micro level or decreasing the spacing between adjacent components.
Therefore, high-density mounting is being achieved by stacking module circuit boards three dimensionally. For example, spacer 1360 of patent document 1 and connecting chip 1550 of patent document 3 connect a land formed on the top surface of a glass epoxy circuit board with the corresponding land formed on the bottom surface of the other glass epoxy circuit board three-dimensionally through via holes 1320. However, spacer 1360 and connecting chip 1550 are used only to connect module circuit boards opposed to each other electrically and mechanically, and are not mounted with any electronic components such as semiconductor elements thereon.
In a case where clips or bolts are used to fix the module circuit boards stacked as in patent document 2, the area allowed for the mounting decreases with increasing area occupied for the provision of the fixing and connecting members.
In addition, an increase in the number of connecting terminals between the module circuit boards increases the area taken up for the connecting connectors in the connection of the module circuit boards.
Thus the increase in the area for the connection between the module circuit boards prevents an improvement in mounting density.
Furthermore, in order to improve EMC properties, Japanese Patent Laid-Open Application No. H05-29784 (hereinafter referred to as patent document 4) uses a metal case, whereas Japanese Patent Laid-Open Application No. H07-30215 (hereinafter referred to as patent document 5) uses a metal board subjected to an insulating treatment, thereby shielding module circuit boards from electromagnetic waves or the like.
However, such shielding with a metal case or an insulating metal board for EMC measurements in line with high-speed and high-frequency electronic devices has the following problems.
In patent document 4, the metal case is an additional part for shielding electromagnetic waves and causes an increase in the weight and volume of electronic devices, going against the trend toward miniaturization. In addition, high-density component mounting requires the metal case undergoing an insulating treatment, similar to the metal board.
In patent document 5, the insulating metal board subjected to the insulating treatment leads to an increase in the weight and volume of electronic devices, similar to the metal case of patent document 4. In addition, it is impossible to completely shield the radiation of unnecessary electromagnetic waves or the intrusion of external noise through the gaps of the corner posts because these are where the top and bottom insulating metal boards are connected with each other.